Gripper assembly for a coiled tubing injector

ABSTRACT

A gripper assembly for a coiled tubing injector is provided. The assembly comprises a gripper block coupled to a carrier at a working position using complementary mating structures. The assembly further comprises a releasable locking structure which secures the gripper block to the carrier at the working position and prevents displacement of the gripper block from the carrier during operation. In a locking position of the locking structure, at least one component of the locking structure extends between the carrier and the gripper block to contact a receiving component in the carrier or the gripper block for preventing decoupling of the gripper block from the working position. A release tool for actuating the locking structure to a released position for disengaging the gripper block from the carrier is also provided.

FIELD

The present disclosure relates generally to gripper assemblies forcoiled tubing injectors, more particularly to a lock/release methodtherefor.

BACKGROUND

It is well known that injectors are widely used in the oil and gasindustry to run coiled tubing into or out of wellbores for performingdifferent downhole operations, such as workover services, drilling,completions, and production. A gripper assembly is an important part ofa coiled tubing injector and is used to engage and grip the coiledtubing for forcibly inserting and withdrawing a continuous length ofcoiled tubing into or out of oil and gas wellbores.

Generally, the injector is supported in a mast over a wellbore. Acontinuous length of coiled tubing is spooled and supported on a reel,and is fed to the injector via an arced guide or gooseneck. The injectorutilizes series of gripper assemblies mounted on a pair of opposingendless chains to grip the coiled tubing.

FIGS. 1A and 1B illustrate a typical coiled tubing injector, generallyindicated by reference number 10. Injector 10 includes two hydraulicmotors 12, a pair of drive sprockets 14, a pair of idler sprockets 16, apair of endless chains 18, chain tension cylinders 20, skate chains 21around skate bars 22 driven by a group of skate traction cylinders 24.Each endless chain 18 is mounted between one drive sprocket 14 and oneidler sprocket 16, and is tensioned by a respective chain tensioncylinder 20 connected to the idler sprocket 16. Each endless chain 18also carries a series of gripper assemblies 26.

The pair of skate chains 21 under pressure of skate bar 22 forciblyurges pairs of opposing gripper assemblies 26 together, applyinggripping forces, to grip the coiled tubing in therebetween. Meanwhile,the gripper assembly is driven by the pair of endless chains 18, 18. Asa result, the coiled tubing, represented by the broken line in FIG. 1Bis forced to move downward or upward over the wellhead, inserting orwithdrawing the coiled tubing respectively, into or out of the wellbore.

A conventional gripper assembly is usually a plurality of one piece,unitary blocks, mounted to the opposing endless chains 18, 18. Thechains rotate in opposing directions and are arranged to meet along alinear portion arranged inline over the wellhead. Each block has agripping surface, a central portion of which has a profile shaped forgripping coiled tubing. The profile may be semi-circular, V-shape orcombined curved and planar cross-sectional profile for engaging the coiltubing between its profile and its opposing block's profile. In opposingarrangement, opposing blocks form an obround, diamond or hybrid grippingprofile. Each or inline adjacent blocks are connected to another blockby connecting links of a conventional chain. Such prior art gripperblocks are disclosed in U.S. Pat. No. 3,258,110 to Pilcher, U.S. Pat.No. 5,094,340 to Avakov, U.S. Pat. No. 5,853,118 to Avakov and U.S. Pat.No. 6,230,955 to Parks.

During operation, the gripping surface of the gripper blocks can wearand can get damaged due to repetitive engagement with coiled tubing.Replacement of old gripper blocks for new is often required. Inaddition, various diameters of coiled tubing require different sizes ofprofiles and gripper blocks. Therefore, the gripper block must befrequently replaced due to damage or to accommodate a change in tubingdiameter or insertion of a downhole tool. In case of wear, a whole newset of different sizes of gripper blocks may be needed to replace allthe old gripper blocks. However, the above mentioned unitary gripperblocks are connected directly through the linkage of the chain. In orderto replace the worn or damaged gripper block with a new one, a fewadjacent linkages of the chain have to be disassembled first. Then theworn or old gripper block can be released from the chain and furtherreleased from adjacent gripper blocks. The installation procedure isopposite to the above disassembling procedure. The whole operation iscomplex and time-consuming.

Various improvements have been made to gripper block designs for ease ofreplacement in field operation. One such design is a gripper assemblyincluding a carrier mounted on the chain and a releasable gripper shoecarried in the carrier. One simple means for fastening the gripper shoeto the carrier is to use pins or screws. An example of this type ofgripper assembly is disclosed in U.S. Pat. No. 6,892,810 to Austbo etal. The gripper assembly comprises a block body, a gripper plateconnected with the block body by pins, and a flex layer disposed betweenthe gripper plate and the block body to allow the gripping surface ofthe gripper plate to move relative to the block body. This relativemovement allows the gripping surface of the gripper block to rapidlyconform to changes in the outer diameter of coiled tubing.

Other designs have also been developed to improve the performance of thegripper assembly. U.S. Pat. No. 6,173,769 to Goode discloses a gripperassembly having a carrier and a removable gripping shoe mounted to thecarrier. The removable shoe includes a plurality of tongues for slidinginto slots formed on the carrier, and is floated on the carrier byinserting an elastomeric pad sandwiched between the carrier and shoe. Amanually depressible spring along one side of the carrier prevents theshoe from sliding out of the slots during operation of the injector.

U.S. Pat. No. 8,191,620 to Maschek, Jr. et al. discloses a gripperassembly comprising a carrier for securing the gripper to the chaindrive mechanism of the coiled tubing injector unit and a gripping shoecarried by the carrier. The gripper shoe has at least one downwardlyextending leg carrying an inwardly projecting tab. The inwardlyprojecting tab and downwardly extending leg cooperates with the carrierto preclude lateral movement of the gripper shoe while permittingrotational movement of the gripper positioned on the carrier. Theconfiguration of the gripper assembly permits quick and easy removal andreplacement of the gripper block.

Although various improvements have been made to various gripperassemblies for facilitating installation and removal in operation, thereis still significant time and expense required.

There is still room for alternatives or improved gripper assemblies thatare easy to maintain and replace with additional savings in time andcost.

SUMMARY

Embodiments disclosed herein provide a securing or locking arrangementwhich secures a gripper block at a working position on a carrier andwhich prevents displacement of the gripper block from the carrier. Thegripper block is coupled to the carrier at the working position usingcomplementary mating connectors or structures supported on the carrierand the gripper block. The securing arrangement prevents detachment ofthe coupling arrangement thereby ensuring retention of the gripper blockat the working position during operation.

Embodiments described herein also describe a release tool for disablingthe securing arrangement for disengaging the gripper block from thecarrier.

Accordingly, in one broad aspect a gripper assembly for use in a coiledtubing injector for injecting and withdrawing a length of coiled tubinginto and from a well along a moving direction is provided. The gripperassembly comprises a carrier having a mounting surface and a backsurface. The carrier is driveably mounted to a gripper chain at the backsurface thereof. The gripper assembly further comprises a gripper blockhaving a gripping surface for receiving the coiled tubing and anattachment surface. The gripper assembly also comprises a sliding jointformed between the carrier's mounting surface and the gripper block'sattachment surface and extending transverse to the moving direction. Thegripper block is slidable along the sliding joint for coupling thegripper block at a working position within the carrier for gripping thecoiled tubing. The gripper assembly also comprises one or morereleasable locking pins. Each locking pin has a corresponding recess.Each locking pin and corresponding recess is aligned between the carrierand the gripper block for extension of the locking pin to the lockingposition for securing the gripper block from decoupling from the workingposition.

Accordingly, in another broad aspect a method for releasably securing agripper block to a carrier driven by a coiled tubing injector isprovided. The method comprises coupling the gripper block at a workingposition within the carrier by slidably engaging complementary matingstructures between the gripper block and the carrier. The method furthercomprises aligning at least one recess in one of the gripper block andthe carrier with a pin extending from the other of the carrier and thegripper block. Finally, the method comprises engaging each pin with acorresponding recess for securing the gripper block from decoupling fromthe working position. In one embodiment, the coupling step furthercomprises installing one or more of the locking pins through one or morepin bores in a mounting surface of the carrier. The coupling stepfurther comprises sliding an attachment surface of the gripper blockalong the carrier's mounting surface. The sliding movement actuates theone or more locking pins into a retracted, released position within theone or more pin bores and between the gripper block's attachment surfaceand the carrier's mounting surface. The sliding movement also allows thecomplementary mating structures to cooperate and engage for coupling thegripper block at the working position. The coupling also aligns the oneor more pin bores with one or more recesses provided on the gripperblock's attachment surface for engagement with the one or more recessesfor securing the gripper block at the working position.

Accordingly, in another broad aspect a release tool for disengaging agripper block secured to a carrier of a gripper assembly described inthe foregoing paragraphs is provided. The tool comprises a frame havinga handle and a base configured to be supported in a stationary positionon the gripper block. The tool further comprises one or more projectionsextending out from the base. The one or more projections are configuredand spaced to operatively engage with the one or more locking pinsextending through the gripper block for actuating the one or morelocking pins into their released position to allow the gripper block toslide out of the carrier.

Accordingly, in another broad aspect a method for disengaging a gripperblock secured to a carrier mounted on a gripper chain of a coiled tubinginjector using a release tool is provided. The method comprisessupporting a base of the release tool on the gripper block using ahandle of the release tool to disengage the gripper block from thecarrier. The gripper block is coupled and secured at a working positionwithin the carrier using one or more locking pins extending between thegripper block and the carrier and extending through an attachmentsurface of the gripper block. The method further comprises pushing therelease tool using the handle to enable one or more projectionsextending out from the base to contact and displace the one or morereleasable locking pins extending through the attachment surface into aretracted, released position which enables disengagement of the gripperblock from the carrier. Finally, the method comprises lifting thedisengaged gripper block off the carrier using the handle. In oneembodiment, before securing the gripper block to the carrier, thegripper block is coupled at the working position by aligning andengaging complementary mating structures supported at a mounting surfaceof the carrier and the gripper block's attachment surface. Further, inone embodiment, the disengagement step further comprises misaligning anddisengaging the complementary mating structures before lifting thedisengaged gripper block.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described more fully with reference to theaccompanying drawings in which:

FIG. 1A is a perspective view of a traditional coiled tubing injectorhaving prior art coiled tubing grippers;

FIG. 1B is a cross-section view along 0-0 of FIG. 1A;

FIG. 2 is a perspective view of a series of gripper assemblies mountedon a portion of an endless chain with one gripper assembly explodedaccording to a first embodiment of the present invention;

FIG. 3 is an exploded view of the gripper assembly of FIG. 2 viewed fromtop;

FIG. 4 is an exploded view of the gripper assembly of FIG. 2 viewed frombottom;

FIG. 5 is a cross-section view of the gripper block in FIG. 3 along A-A;

FIG. 6 is a cross-section view of the gripper block of FIG. 5 along B-B;

FIG. 7 is a side view of the carrier of FIG. 3;

FIG. 8 is a cross-section view of a releasable locking pin of thegripper assembly of FIG. 3;

FIG. 9A is a perspective view of the gripper assembly of FIG. 3 showingpositioning of the gripper block on the carrier at the start of acoupling and locking process;

FIG. 9B is a side view of FIG. 9A;

FIG. 9C is a cross-section view of FIG. 9B along D-D;

FIGS. 9C1 to 9C5 are schematic cross-section views illustratingpositioning of the gripper block with the carrier during the couplingand locking process,

FIG. 9C1 shows position of the gripper block and the carrier just beforethe gripper block is positioned on the carrier, in this position thecomplementary mating structures provided on the gripper block and thecarrier are misaligned,

FIG. 9C2 illustrates the gripper block positioned on the carrier, inthis position one of the releasable locking pins is displaced by atrailing end of the gripper block into its retracted position enablingtravel of the gripper block along the carrier,

FIG. 9C3 illustrates another of the releasable locking pins beingcontacted by a leading end of the gripper block for its displacementinto a retracted position,

FIG. 9C4 illustrates a position where the mating structures on thegripper block and the carrier are almost aligned and where the lockingpins are almost aligned with recesses in the gripper block, and

FIG. 9C5 illustrates a position where the mating structures on thegripper block and the carrier are aligned and where the locking pinsengage the recesses in the gripper block;

FIG. 10A is a perspective view of the gripper assembly of FIG. 3,showing positioning of the gripper block on the carrier after thegripper block has been coupled and locked to the carrier, in thisposition complementary mating structures on the gripper block and thecarrier engage with each other;

FIG. 10B is a cross-section view of FIG. 10A along I-I;

FIG. 11 is a perspective view of a release tool;

FIG. 12A is a cross-section view of the release tool of FIG. 11 at aposition to start release of the gripper block;

FIG. 12B is a cross-section view of the release tool of FIG. 11 at aposition when the gripper block is ready to release;

FIG. 13A is a perspective view of an alternative of the release tool;

FIG. 13B is a cross-section view of FIG. 13A;

FIG. 14 is a perspective view of another example of a gripper block;

FIG. 15 is a perspective view of another example of a gripper block;

FIG. 16 is a perspective view of further another example of a gripperblock; and

FIG. 17 is a top view of the gripper block of FIG. 2 illustrating analternative location of a locking mechanism.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 2 to 10B illustrate a gripper assembly used in a general coiledtubing injector to engage and grip coiled tubing for inserting andwithdrawing continuous length of coiled tubing into or out of wellboresaccording to embodiments described herein. As shown in FIG. 2, aplurality of gripper assemblies 1000,1000 . . . are arranged in a seriesabout each of a pair of opposing endless chains 2000,2000 of a coiledtubing injector 10. Each gripper assembly 1000 is driven by respectivechain 2000 in opposing relation to another opposing gripper assembly1000 driven by its respective opposing chain 2000, gripping andsandwiching the coiled tubing therebetween. Other driving arrangementsmay be known to which the gripper assemblies 1000 can be driveablesupported.

In FIG. 2, a portion of conventional endless chain 2000 is shown withgripper assemblies 1000 installed thereto. One gripper assembly alongwith its associated chain is disassembled to show details of eachcomponent. It can be seen that each unit of the chain 2000 includes apair of slip plates 2002, two pairs of roller links 2004, a press plate2006, a master link 2008 and a pair of cotter pins 2010. Master link2008 inserts through the roller links 2004, the slip plates 2002,carrier 1300 and press plate 2006. Cotter pins 2010 are then insertedinto the holes in the master link 2008 to fasten the carrier to thechain.

With reference to FIGS. 3 and 4, the gripper assembly 1000 comprises agripper block 1100, a carrier 1300, a locking mechanism 1500 forreleasably securing gripper block 1100 to carrier 1300 for ease of blockreplacement. Locking mechanism 1500, in this embodiment, includes twospring plungers or locking pins 1502 a and 1502 b that are fastened tothe carrier 1300.

Herein, relative orientation can be termed as corresponding to andrelative to the moving direction of travel of the coiled tubing into andfrom a well, namely being inline axis along axis Z-Z. The gripper block1100 imposes normal forces to the coiled tubing, being perpendicular andnormal to the inline axis Z-Z. The gripper block 1100 is slidablyinstalled to the carrier 1300 in a direction perpendicular andtransverse to the inline axis Z-Z.

With further reference to FIG. 3 to FIG. 6, each gripper block 1100comprises a concave gripping surface 1112, a back side or attachmentsurface 1114, a pair of side surfaces 1116 a and 1116 b, and a pair ofleading and trailing facets 1118 a and 1118 b. Best seen in FIG. 4, tworecesses 1130 a and 1130 b are formed in the attachment surface 1114 andtransversely spaced therealong for receiving the two corresponding andtransversely spaced locking pins 1502 a and 1502 b installed in thecarrier 1300. In one embodiment, the gripper block 1100 comprises tworelease passages 1130 a′ and 1130 b′ extending through the gripper blockfrom a side surface to a corresponding recess 1130 a,1130 b in theattachment surface.

Gripping surface 1112 extends between the two facets 1118 a and 1118 b,for forming a substantially continuous gripping surface with adjacentand opposing blocks 1100, 1100. The gripping surface 1112 has a concavesemi-circular, V-shape or compound profile along a cross-section ornormal plane X-Y perpendicular to a moving direction of the coiledtubing into and from a well, as indicated by inline axis Z-Z, in orderto accommodate the coiled tubing. Gripping surface 1112 can have aplurality or transverse wickers or parallel grooves 1120 spaced alongthe surface 1112 to aid in gripping coiled tubing, each extending alongplane X-Y as disclosed in the prior art, such as in U.S. Pat. No.5,853,118, U.S. Pat. No. 6,230,955 and U.S. Pat. No. 8,191,620.

The gripping surface 1112 preferably has relatively large rounded edges1113 a and 1113 b at the end of the gripping surface 1112. In thisembodiment, the radius of the rounded edge is up to ⅜″. When a gripperassembly is driven by its respective chain and moves away from the drivesprocket to start engaging the coiled tubing, or moves close to thedrive sprocket to start disengaging the coiled tubing, the gripper blockwill tilt and rotate around the sprocket in this transition area. Theend portion of the gripping surface will tend to apply extra grippingforces to the coiled tubing due to the rotation. Having a relative largerounded edge at the end portion of the gripping surface leaves a biggerclearance or space for coiled tubing in this transition area. Itprevents the coiled tubing being affected or damaged by the end portionof gripper surface, meanwhile ensuring the coiled tubing beingeffectively gripped by the gripping surface 1112.

Referring to FIG. 4, attachment surface 1114 is located along atransverse plane along an opposite side of the gripper block 1110 fromthe gripping surface and engages with the corresponding mounting surface1302 a of carrier 1300. The attachment surface 1114 and mounting surface1302 a form an interlocking joint that enables sliding couplingtransverse to the inline loading direction, yet forms a secureconnection to retain the gripper block 1100 to the carrier 1300 duringoperation. In one embodiment, the interlocking joint is formed by maleand female sliding joints supported at the carrier's mounting surface1302 a and the gripper block's attachment surface 1114. Attachmentsurface 1114 includes a mainly flat surface 1122 suitable to transferloads from the gripper block 1100 to the carrier 1300. Further, theattachment surface 1114 further comprises two depending edges 1124 a and1124 b projecting out rearwardly from the flat surface 1122 andextending along the transverse X direction, which is perpendicular tothe coiled tubing moving direction Z-Z. Edges 1124 a and 1124 b projectout rearwardly from the gripper block 1100 for overlapping and couplingwith the carrier 1300. Each edge 1124 a, 1124 b further comprises one ormore inwardly-extending lips 1126 a, 1126 b, 1126 c and 1126 d. On eachside, the inwardly-extending lips 1126 a, 1126 b and 1126 c and 1126 dare spaced apart a distance along each edge.

Complementary interlocking joint structures are supported by the carrier1300. The carrier 1300 has corresponding and cooperating side portions1306 a and 1306 b. Each side portion 1306 a,1306 b has twooutwardly-extending lips 1314 a,1314 b corresponding to the respectiveinwardly-extending lips 1126 a,1126 b. On each side portion 1306 a, 1306b, the outwardly-extending lips 1314 a,1314 b are spaced apart adistance along each edge. The spacing between lips 1126 a, 1126 b andlips 1314 a,1314 b are complementary so as to permit perpendicularpassage therethrough when misaligned to couple the edges and sideportions.

Misaligned, the inwardly-extending lips 1126 a,1126 b slideably couplerearward of the outwardly-extending lips 1314 a,1314 b respectively.Aligned, the lip 1126 a slides to engage lip 1314 a and lip 1126 bslides transversely to engage lip 1314 b to interlock and retain thegripper block 1100 from perpendicular release therefrom.

The lip-interlocking joint structure can be in the form of a dovetailjoint wherein the lips have complementary wedge-shaped elements. In thisdisclosure, for ease of description, the dovetail portion of thedovetail joint in the gripper block 1100 is defined as a female dovetailfor distinguishing them from the dovetail portions supported on thecarrier 1300. The dovetail portions in the carrier 1300 are defined asmale dovetails. Of course, those skilled in the art understand thatfemale dovetails can be arranged in the carrier, and male dovetails canbe arranged in the gripper block. Also, a person of skill in the artwill recognize that any form of complementary mating structures can besupported by the gripper block 1100 and carrier 1300 for slidablycoupling the gripper block 1100 from a released position to a coupledworking position on the carrier 1300. As used herein, the term “workingposition” means an operative position or condition wherein thecomplementary mating structures provided on the gripper block 1100 andthe carrier 1300 are coupled or engaged so as to align the profiledcentral portions on opposing gripper blocks, during operation, to gripthe coiled tubing. In the working position, the gripper block 1100cannot be removed by forces normal to the Z-Z direction.

In this embodiment, there are two female dovetails spaced apart adistance along each edge of gripper block 1100, female dovetails 1126 aand 1126 b located along edge 1124 a, and dovetails 1126 c and 1126 dlocated along edge 1124 b. The inner surface of each female dovetail asshown in FIG. 5, in this embodiment, is 60 degrees with respect to theflat surface 1122. However, those skilled in the art understand thatother degrees of angle, such as 30 degrees or 45 degrees can be chosen.The length of each female dovetail is configured less than acorresponding recess in carrier 1300 so that the female dovetails can belowered down through the recesses and slide into corresponding maledovetails in carrier 1300. The dovetail engagement between the gripperblock and the carrier transfers inline injection forces from carrier1300 to gripper block 1100, and transfers reactive forces back intocarrier 1300. The dovetails provide a tight engagement between thegripper block and the carrier for efficient force. The tight engagementprevents inline movement or inline displacement of the gripper block1100 on the carrier 1300. As used herein, “inline displacement” meansdisplacement along axis Z-Z in FIG. 2 or travel of the endless chain.However, during operation, the gripper block 1100 is releasably retainedto the carrier 1300 in a direction transverse to the direction of travelor movement of the endless chain. In other words, due to the nature ofthe transverse coupling unless restrained, there would be a chance ofthe mating structures decoupling or disengaging. It is, therefore,necessary to transversely secure the gripper block 1100 to the carrier1300 at the working position to prevent decoupling of the matingstructures. Decoupling is prevented using a retractable lockingstructure.

In an embodiment the locking structure is one or more preloadedretractable locking pins 1502 a and 1502 b which engage correspondingrecesses 1130 a,1130 b which preclude movement of the gripper block 1100from or within the carrier 1300.

Referring to FIG. 4 again, the gripper block 1110 is further providedwith a pair of ramps 1128 a and 1128 b which are machined at theintersections between the flat surface 1122 and each of the sidesurfaces 1116 a and 1116 b, and are located beside the recesses 1130 aand 1130 b. It is preferred that each ramp is about 25 degrees withrespect to the flat surface 1122, as shown in FIG. 6. The ramps are usedto engage and gradually depress the preloaded plungers or locking pins1052 a, 1052 b when the gripper block 1100 starts sliding transverselyinto the carrier during installation which will be described in detailin the following paragraphs.

Side surfaces 1116 a and 1116 b are located between back side 1114 andgripping surface 1112. Material of the block that is not activelyrequired for strength or function can be removed for reducing overallweight of the gripper block 1100. In this embodiment, each side surface1116 a, 1116 b can slope inwardly from the attachment surface 1114towards gripping surface 1112, reducing weight still further, as thegripping surface 1112 can be smaller than the attachment surface 1114.However, it is appreciated by those skilled in the art that theconfiguration of side surfaces 1116 a, 1116 b can depend on the size andstrength requirement of the gripping surface. If the size of grippingsurface 1112 is greater than that of the attachment surface 1114, sidesurfaces 1116 a, 1116 b may slope or diverge outwardly from theattachment surface 1114 towards gripping surface 1112.

Now again referring to FIGS. 3, 4 and 7, carrier 1300 comprises a basebody 1302 having a flat mounting surface 1302 a, a flat back surface1304, a pair of side portions 1306 a and 1306 b, and a pair of leadingand trailing facets 1308 a and 1308 b. The mounting surface 1302 a formsa supporting surface for attachment surface 1114 of gripper block 1100.The carrier's flat back surface 1304 rides on the skate chain 21 asshown in FIG. 2 to transfer gripping forces from the skate bar to thegripper block 1100. The back surface 1304 may be mounted on the skatechain 21 using conventional mounting arrangements known to those ofskill in the art.

Complementary mating structures supported by the carrier 1300, in thisembodiment, comprises at least one male dovetail on each side portion1306 a and 1306 b. In this embodiment, there are two male dovetailsalong each side portion 1306, corresponding to the respective femaledovetails on gripper block 1100. Male dovetails 1314 a and 1314 b arelocated along side portion 1306 a, and male dovetails 1314 c and 1314 dare located along side portion 1306 b. Two male dovetails along the sameside portion are spaced apart a distance, forming an indent ordepression therebetween. Indent 1334 a is formed between male dovetails1314 a and 1314 b on side portion 1036 a, and indent 1334 d is formedbetween male dovetails 1314 c and 1314 d on side portion 1036 b. Twomale dovetails on each side portion are located in the middle part ofthe side portion. Therefore, two end indents are formed. In thisembodiment, end indents 1334 b and 1334 c are located on side portion1306 a, and end indents 1334 e and 1334 f are located on side portion1306 b. The inner surface of each male dovetail has 60 degrees withrespect to the mounting surface 1302 a as shown in FIG. 7, same as itsmatching female dovetail in gripper block 1100. The length of each maledovetail is preferred to match with that of the corresponding femaledovetail on gripper block 1100.

A locking arrangement of corresponding recesses 1130 a, 1130 b andlocking pins 1502 a, 1502 b releasably locks the gripper block 1100 tocarrier 1300. The locking pins releasably extend between the gripperblock 1100 and carrier 1300 to a locking position to engage acorresponding recess. In one embodiment, the carrier 1300 furthercomprises two threaded holes or pin bores 1310 a and 1310 b extendingthrough the base body from back surface 1304 to mounting surface 1302 a.Two releasable locking pins 1502 a and 1502 b can be threaded into thetwo pin bores respectively from back surface 1034 until the heads 1503of the locking pins project out from the mounting surface 1302 a. Whenpressed or depressed, the heads 1503 of the locking pins 1502 retractbelow the mounting surface 1302 a to a released position enablingsliding in or sliding out of the gripper block 1100 on the carrier 1300.An example of the locking pins used in this embodiment is shown in FIG.8. Locking pin 1502 is a spring loaded pin for biasing the head 1503 ofthe locking pin 1502 into the locking position. The locking pin 1502further comprises a lock element 1504, such as an outwardly projectingdistortable nylon pellet formed in its threaded body. Duringinstallation, the lock element 1504 is forced into the threaded pin borewherein it tightens the thread engagement between the locking pin andthe carrier.

As explained earlier, the carrier 1300 can be mounted to skate chain2000 in various ways. In one embodiment, in order to connect the carrier1300 to the chain 2000, the carrier 1300 is provided with two additionalthrough holes 1312 a and 1312 b that extend through base body 1302between the leading and trailing facets 1308 a and 1308 b. As discussedabove, the carrier 1300 is secured to the chain by inserting master link2006 through holes 1308 a and 1308 b, and slip plate 2002, roller link2004 and press plate 2006 by known traditional methods.

FIG. 4 illustrates one embodiment for avoiding interference of twoadjacent carriers 1300 when the gripper assembly tilts in the transitionarea close to the sprocket. As shown in FIG. 4, carrier 1300 has atongue 1330 and a pair of spaced apart ears 1332 a and 1332 b projectingout from side portions. The space between the pair of ears 1332 a and1332 b is adapted to receive a tongue of an adjacent carrier. It ispreferred that the front facing surfaces 1331 a of the tongue, andsurfaces 1331 b and 1331 c of the pair of ears 1332 a and 1332 b aretapered from the base body to outside. In this embodiment and withreference to FIG. 7, the tapered angle is 45 degrees.

The following paragraphs, with reference to FIGS. 3 through 10B,describe in detail the coupling and securing process. At a higher level,the method or process comprises sliding the gripper block 1100transversely along a sliding joint between the carrier's mountingsurface 1302 a and the gripper block's attachment surface 1114 to enableslidable engagement or coupling of corresponding mating structuressupported by the carrier's mounting surface 1302 a and the gripperblock's attachment surface 1114. The gripper block 1100 is therebycoupled at the working position within the carrier 1300. The couplingprocess aligns the recesses 1130 a and 1130 b in the gripper block'sattachment surface 1114 with the locking pins 1502 a and 1502 bextending from the pin bores 1310 a and 1310 b in the carrier's mountingsurface 1302 a. The gripper block 1100 is secured to the carrier 1300 bythe locking pins 1502 a and 1502 b engaging their respective recesses1130 a and 1130 b. The engagement prevents decoupling of the gripperblock 1100 from the carrier 1300 at the working position andsubsequently displacement of the gripper block from the carrier.

In an embodiment, the process first comprises applying a coating of anadhesive to the threaded surface of the two locking pins 1502 a and 1502b, such as Loctite® Retaining Compounds for filling the space of thethreads. The locking pins are then screwed into the two pin bores 1310 aand 1310 b of carrier 1300 from back surface 1304 until their headsproject out of the mounting surface 1302 a. After the adhesive is cured,they form a strong connection and avoid inadvertent unthreading from thepin bores 1310 a and 1310 b. In one embodiment, the pin bores 1130 a and1130 b are stepped and have retaining shoulders (not shown). Theposition of each of the locking pins 1502 a and 1502 b with respect tocarrier 1300 in the corresponding threaded pin bores 1330 a and 1330 bis limited by the lock element 1504. Alternatively, the pin itself isstepped with the threaded portion having a larger diameter than thehead-retaining portion for installation in a stepped pin bore. Theadhesive applied to the pins 1502 a and 1502 b also aid in the lockingprocess. The carrier 1300 is then mounted on the chain by the methoddescribed above. The carrier is now ready to receive the gripper block1100. The locking pins 1502 a and 1502 b on the carrier 1300 are in aninitial extended, locking position.

In order to avoid premature engagement of the locking pins 1502 a and1502 b with the recesses 1130 a and 1130 b, during the installationprocess, in this case, the complementary mating structures on thecarrier 1300 are offset from the mating structures on the gripper block1100. This arrangement enables the gripper block 1100 to travel alongthe carrier 1300 by a short distance before the mating structures arealigned and before the locking pins 1502 and the recesses 1130 arealigned. As seen in FIG. 9C1, the two female dovetails on each sideportion of gripper block 1100 are relatively aligned with theircorresponding indents of the carrier 1300. In other words, femaledovetail 1126 a relatively aligns with end indent 1334 b, and femaledovetail 1126 b relatively aligns with middle indent 1334 a, the same asthe other side portion. Meanwhile, the male dovetails on carrier 1300also relatively align with the corresponding indents in gripper block1100. As seen in FIG. 9C2, the gripper block 1100 is then lowered downon the attachment surface 1114 so that one of the locking pins 1502 a ispressed by the attachment surface 1114 into a retracted, releaseposition. Note that herein the locking and released position of thelocking pins includes the biased operation of the pin heads 1503.

Once pin 1502 a is fully retracted below or under the carrier's mountingsurface 1302 a, the gripper block's attachment surface 1114 contactswith the carrier's mounting surface 1302 a. The gripper block 1100 isable to slide along the mating structures and move forward in adirection indicated by E. As seen in FIGS. 9C3 and 9C4, as the gripperblock 1100 starts moving, one of the ramps 1128 b on the gripper block1100 contacts the head of the other locking pin 1502 b, and graduallypresses the head until it is fully retracted into a released positionunder the mounting surface 1302 a. In this position, the matingstructures on the carrier 1300 and the gripper block 1100 are almostaligned and the locking pins 1502 a and 1502 b are almost aligned withrecesses 1130 a and 1130 b. FIGS. 9C5 and 10B illustrate a positionwhere the gripper block 1100 is coupled and secured to the carrier 1300.In this position, the mating structures supported by the carrier 1300and the gripper block 1100 are aligned and cooperate with each other tocouple the gripper block 1100 at the working position within the carrier1300. In other words, female dovetails 1126 a, 1126 b, 1126 c and 1126 don gripper block 1100 fully engage with male dovetails 1314 a, 1314 b,1314 c and 1314 d on carrier 1300, respectively. The coupling alsoaligns the recesses 1130 a and 1130 b with the locking pins 1502 a and1502 b, respectively, so that the heads of the locking pins 1502 a and1502 b are able to extend and project into the recesses 1130 a and 1130b under the restoring forces of the pre-loaded spring. Engagement of thelocking pins within the recesses, secures or locks the gripper block1100 to the carrier 1300 as shown in FIGS. 10A and 10B. The dovetailengagement between the gripper block 1100 and the carrier 1300 preventsmovement of the gripper block 1100 from the carrier 1300 and enablestransfer of inline forces from the carrier 1300 to the gripper block1100 and subsequently to coiled tubing for pushing or pulling the coiledtubing in or out of a well. The locking pins 1502 a and 1502 b engagingthe gripper block 1100 prevent sliding decoupling of the gripper block1100 from the carrier 1300.

Premature engagement of the locking pins 1502 a and 1502 b with therecesses 1130 a and 1130 b, during the installation process, may also beavoided by locating the pin bores 1310 and the corresponding recesses1130 on the carrier 1300 and in the gripper block 1100, respectively, inan offset arrangement. The offset arrangement defines two differentcoupling paths spaced along Z-Z which ensures that a locking pin doesnot contact the wrong recess during the gripper block's 1100 travel onthe carrier 1300. In this arrangement the gripper block 1100 can slidetransversely entirely along the width of the carrier 1300.

The following paragraphs describe a release tool and a method of usingthe release tool for disengaging the gripper block 1100 from the carrier1300. FIGS. 11 through 12B show one embodiment of the release tool.Release tool 3000 comprises a frame or body 3002, two projectionsextending out from the frame 3004 a and 3004 b and a handle 3006. Theframe has a flat bottom surface for engaging with gripper block 1100. Inthis embodiment, projections 3004 a and 3004 b have threads on one endso that each projection is fastened to the frame by a nut on this end.The other end extends out from the bottom surface of the frame. Thelength of the extended portion under the bottom surface is the same asthe height of gripper block 1100, indicated by H in FIG. 12A. Thediameter of the projection is smaller than the diameter of the releasepassage 1130. When the release tool 3000 is pushed so that the flatbottom surface contacts the gripping surface, the projections extendinto the release passages of gripper block 1100. The locking pins arepressed by the projections against the pre-loaded springs and aredisplaced out of the release passages and under carrier's mountingsurface 1302 a into the retracted, released position. Horizontal forcesare then applied to the release tool to move the gripper block 1100along with the release tool 3000 along direction F. The gripper block1100 slides along the dovetails until the gripper block is decoupled.The decoupled position is shown in FIG. 12B. The gripper block 1100 cannow be lifted up and released from the carrier 1300.

In the embodiment illustrated in FIGS. 11 to 12B, frame 3002 of releasetool 3000 includes a U-shaped plate 3010 and two side plates 3012 a and3012 b. The two side plates can be welded or secured to the U-shapedplate using known methods. The handle 3006 is a hollow cylindrical barinstalled between the two side plates which reduces the total weight ofthe release tool and provides an easy grip.

The configuration of the release tool in not limited to the particularconfiguration shown in FIG. 11. It will be appreciated by those skilledin the art that as long as there are two projections having a samelength as the height of the gripper block and are able to enter therelease passages provided in the gripper block, various modificationscan be made without departing from the concept. For example, FIGS. 13Aand 13B show an alternative embodiment of the release tool. The frame ofthe release tool shown in FIGS. 13A and 13B is a plate 3010 and thehandle 3006 of the release tool is a cylindrical bar protruding out ofthe plate. The two projections 3004 b,3004 b are directly screwed to thebody.

Although the gripper assembly illustrated in FIGS. 3 to 12B is for 2″coiled tubing, other sizes of coiled tubing, for example from 1″ to3.5″, can also been accommodated using the design disclosed herein byonly changing the size of the central portion in the gripping surface ofthe gripper block. FIGS. 14 to 16 show three different sizes of gripperblock, 1″, 2.875″ and 3.5″. The only change is the radius of the centralportion while other parameters keep the same. As the radius of thecentral portion becomes larger, the positions of the release passagesshift from side surface 1116 to the positions within the centralportion, as shown in FIG. 16.

A person of skill in the art will appreciate that the one or morelocking pins 1502 may be provided in the gripper block 1100 instead ofthe carrier 1300 and the corresponding recesses 1130 may be provided inthe carrier's mounting surface 1302 a instead of the gripper block'sattachment surface 1114. The same release tool 3000 may be used todisplace the locking pins 1502. The release tool 3000 can also besimplified to a small handle and be integrated together with the lockingpin, such as that shown in FIG. 17. During disengagement, the releasetool 3000 is used to pull the locking pins 1502 into corresponding pinbores provided in the gripper block thus enabling decoupling and slidingout of the gripper block from the carrier. In this case, the lockingpins 1502 may be installed after the gripper block 1100 is coupled tothe carrier 1300 at the working position using the same complementarymating structures illustrated in FIGS. 3 and 4. Since the locking pins1502 are installed after the coupling step, there are no chances of thelocking pins prematurely engaging with the recesses 1130 during thecoupling step. Therefore, there is no need for the mating structures onthe carrier and the gripper block to be arranged in an offsetarrangement.

The gripper assembly design according to embodiments described hereinprovides a quick and easy way to install and remove gripper blockswithout disassembling the chain and carriers. It saves time and makesmaintenance and repair easier. Meanwhile with all different sizes ofgripper blocks available, one injector can be quickly configured toperform various services that require different sizes of coiled tubing.It improves the working efficiency of an injector in the field.

Although the embodiments included herein describe two plungers and twopairs of dovetails in each component as the best mode, those skilled inthe art understand that a gripper assembly having one plunger and onepair of dovetails in one component, for example one female dovetail inthe middle on each edge of the gripper block, is sufficient to coupleand secure the gripper block 1100 to the carrier 1300.

Although the embodiments describe that two plungers or locking pins areinstalled from a back surface towards the front mounting surface of thecarrier, the shape and configuration of the plunger or the mountingmethod to the carrier are not limited to these embodiments.

Although embodiments have been described above with reference to theaccompanying drawings, those skilled in the art will appreciate thatvariations and modifications may be made without departing from thescope thereof as defined by the appended claims.

The embodiments of the invention for which an exclusive property orprivilege is claimed are defined as follows:
 1. A gripper assembly foruse in a coiled tubing injector for injecting and withdrawing a lengthof coiled tubing into and from a well along a moving direction, thegripper assembly comprising: a carrier having a mounting surface and aback surface, the carrier being driveably mounted to a gripper chain atthe back surface thereof; a gripper block having a gripping surface forreceiving the coiled tubing and an attachment surface; a sliding jointbetween the carrier's mounting surface and the gripper block'sattachment surface and extending transverse to the moving direction, thegripper block slidable along the sliding joint for coupling the gripperblock at a working position within the carrier for gripping the coiledtubing; and one or more releasable locking pins, each locking pin havinga corresponding recess, each locking pin and corresponding recessaligned between the carrier and the gripper block for extension of thelocking pin to a locking position for securing the gripper block fromdecoupling from the working position.
 2. The gripper assembly of claim1, wherein the sliding joint comprises complementary mating structuressupported at the carrier's mounting surface and the gripper block'sattachment surface.
 3. The gripper assembly of claim 2, wherein thecorresponding mating structures comprise male and female sliding jointssupported at the carrier's mounting surface and the gripper block'sattachment surface.
 4. The gripper assembly of claim 2, wherein thecorresponding mating structures comprise a first dovetail joint portionsupported at the carrier's mounting surface and a second dovetail jointportion supported at the gripper block's attachment surface, the seconddovetail joint portion cooperating with the first dovetail portion forcoupling the gripper block at the working position.
 5. The gripperassembly of claim 1, wherein the gripper block further comprises the oneor more recesses; and the carrier further comprises one or more pinbores extending into the mounting surface for holding the one or morelocking pins, and wherein, in the locking position, the one or morelocking pins extend into the one or more recesses, and in the releasedposition the one or more locking pins are retracted from the one or morerecesses into the mounting surface.
 6. The gripper assembly of claim 1,wherein the gripper block further comprises one or more releasepassages, extending from the gripping surface to a corresponding recessin the attachment surface, for enabling actuation of the locking pinfrom the extended, locking position to the retracted, released position.7. The gripper assembly of claim 6, wherein the locking pin is actuatedfrom the extended, locking position to the retracted, released positionusing a release tool cooperating with the one or more release passagesto displace the locking pin out of the corresponding recess and into themounting surface.
 8. The gripper assembly of claim 1, wherein thegripper block comprises the one or more locking pins and, in the lockingposition, the one or more locking pins retractably extend through pinbores provided in the gripper block's attachment surface to engage thecorresponding recesses to the released position.
 9. The gripper assemblyof claim 8, wherein the one or more locking pins are actuated from thelocking position to the released position using a release toolcooperating with the one or more pin bores to displace the one or morelocking pins out of the corresponding recesses and into the one or morepin bores.
 10. The gripper assembly of claim 1, wherein each locking pinis biased to the extended locking position.
 11. A coiled tubing injectorcomprising a pair of opposing gripper chains; and a plurality of gripperassemblies of claim 1 driven by the pair of gripper chains for running alength of coiled tubing into or from the well along the movingdirection.
 12. A method for releasably securing a gripper block to acarrier driven by a coiled tubing injector, the method comprising:coupling the gripper block at a working position within the carrier byslidably engaging complementary mating structures between the gripperblock and the carrier; aligning at least one recess in one of thegripper block and the carrier with at least one locking pin extendingfrom the other of the carrier and the gripper block; engaging eachlocking pin with a corresponding recess for securing the gripper blockfrom decoupling from the working position.
 13. The method of claim 12,wherein the coupling step further comprises: installing one or more ofthe locking pins through one or more pin bores in a mounting surface ofthe carrier; sliding an attachment surface of the gripper block alongthe carrier's mounting surface, sliding movement actuating the one ormore locking pins into a retracted, released position within the one ormore pin bores and between the gripper block's attachment surface andthe carrier's mounting surface, and allowing the complementary matingstructures to cooperate and engage for coupling the gripper block at theworking position, the coupling aligning the one or more pin bores withone or more recesses provided on the gripper block's attachment surfacefor engagement with the one or more recesses for securing the gripperblock at the working position.
 14. A release tool for disengaging agripper block secured to a carrier of a gripper assembly of claim 1, thetool comprising: a frame, the frame having a handle and a baseconfigured to be supported in a stationary position on the gripperblock; one or more projections extending out from the base, the one ormore projections configured and spaced to operatively engage with theone or more locking pins extending through the gripper block foractuating the one or more locking pins into their released position toallow the gripper block to slide out of the carrier.
 15. The releasetool of claim 14, wherein the one or more projections engage with theone or more locking pins through one or more release passages extendingfrom the gripping surface to its corresponding recess in the attachmentsurface.
 16. The release tool of claim 15, wherein diameter of the oneor more projections is smaller than the one or more release passages toenable entry of the one or more projections into the one or more releasepassages.
 17. The release tool of claim 16, wherein a height of the oneor more projections is substantially equal to a height of the gripperblock.
 18. A method for disengaging a gripper block secured to a carriermounted on a gripper chain of a coiled tubing injector using a releasetool, the method comprising: supporting a base of the release tool onthe gripper block using a handle of the release tool to disengage thegripper block from the carrier, the gripper block being coupled andsecured at a working position within the carrier using one or morelocking pins extending between the gripper block and the carrier andextending through an attachment surface of the gripper block; pushingthe release tool using the handle to enable one or more projectionsextending out from the base to contact and displace the one or morereleasable locking pins extending through the attachment surface into aretracted, released position which enables disengagement of the gripperblock from the carrier; and lifting the disengaged gripper block off thecarrier using the handle.
 19. The method of claim 18, wherein beforesecurement, the gripper block is coupled at the working position byaligning and engaging complementary mating structures supported at amounting surface of the carrier and the gripper block's attachmentsurface and wherein the disengagement step further comprises misaligningand disengaging the complementary mating structures before lifting thedisengaged gripper block.